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Yes, I have a 1990 Mark IV A combo and the OCD works perfectly with the R2 channel :wink: . regards Arno

Hi, since last year I use Fulltone's "OCD" with my MK IV! Although the MK IV actually don't need any OD'S, boost or Distortion pedals, I just tried the OCD, which I bought mainly for use with my other 1-channel tube amps. I must say, that I can get good chrunchy sounds using the OCD with the...

Hi, since January 1991 I'm using my MK IV. I never had a problem with the amp. I don't know problems caused by the EQ. I guess, that the EQ has a amount, even if it is switched off, but in a very positive way, tonewise. Nothing wrong with this, IMO! Arno

One thing to add regarding the graphic EQ. If you look at the schematics of the earlier mark series amps, say from the MK II A, B C+ versions to the MK III, one can see, that the cirquit design of the EQ always is basically the same, but in schematics of the IIA and B you can see relays used...

Hi all, since some years already, I use Mesa's 5881's with my MK IV combo. For my personal taste, the amp sounds less bright as with 6L6's but also with good warms, defination and punch in all 3 channels, al long as playing at moderate volumes. I also tried a pair of Svets from Mesa. IMO, clean...

Hi, I don't think, that the "Class A Section" of the MK IV is cathode biased. According to the schematic I have ( version 08/92 ), the cathodes of the outer power tubes V8 / V9 are connected directly to ground like the inner power tubes V6 / V7 running Class AB. Further they are fixed biased...

Hi, as a owner of a MK IV A too, which I bought new in 1991 in Germany, I remember , that I also had fore a very short time problems with a flickering LED. As far as I remember, it occured while switching from R1 to Lead. First the Lead LED was normal on for short time but then dark for some...

Hi, can you give us some more information about, which EV 12 L's belong to the older and later versions? My MK IV combo from 1990 came stock with the Black Shadow EVM 12 L 200 watts. I also have 3 thiele's loaded with the EVM 12 L`s - OEM version. I also like a lot the Black Shadow MC 90 or...

Hi, my MK IV combo was build in 1990. Over all the years of use I never had a single problem with this amp, appart from tube swapping from time to time, which is normal! This amp is build like a tank. If you really like the sound and the amp is in good all over condition ( look and function ), I...

Hi, My is a MK IV combo loaded with the Black Shadow EVM 12 L. What I like often to do, is to use the combo in combination with a 1x12 open back cab, loaded with the MC 90 or also with a V 30. So one gets best of both worlds in my opinion. The EVM 12 L with it's tight, accurate tone and the...

Hi all, my MK IV is from 1990, Ser. No. IV 0726. It is a export model, power tranny wired for 220 V~ . I purchased the amp in Germany on 2.1.1991! The MK IV uses a lot of LDR's for all the switching jobs. According to a schematic I have ( signed 10-92 ), there are 22 LDR's funktions listed in...

Hi, I fully agree with Russ. I'm also the opinion, that the MK IV already has way enough features. Beside the already mentioned ideas, I would wish a fan, which could be switched off or automatically speed reduced, in order to avoid this nasty disturbing noise, especially for playing with low...

Hi Russ, I tried several of different speakers with my MK IV combo in the past, which still has the stock Black Shadow EVM 12L 200 watt on board. Additional I own 1x12 Thiele cabs loaded with the original OEM EVM 12 L 200 watts, which I use in a stereo configuration with the MK IV, in order...

Hi Russ, how are you, I hope all is well. Regarding the reverb quality of the MK IV. My opinion is, that the reverb of the MK IV isn't weak at all! I would say, it is still one of the best tube reverbs, one can get on board of a tube amp, never had problems with the quality and you know, I...

Hi Tom, my honest opinion........ three posibilities first, the Mesa Boogie sound is simply not jours, then sell the amp and look for another second, beside the tubes something else is wrong with your amp, take it to a good amp tech and fix the problem third, the MK IV is no plug in and...

Hi, according to the mentioned schematic I have, the export model should have a transformer with a 240 V tap. But I can't say it for sure, because until today there was no need to take the chassis out of the combo housing. Regarding the 50 Hz to 60 Hz operating, basically there is a difference...

Hi Tom, what outlet voltage frequency is common in australia? Is it 50 Hz ? I'm not sure if the difference between the net frequenzy in USA ( 60 Hz ) could be the probleme, but it should be considered. Otherwise, if the hum really doesn't come from the speaker or from some other vibrations...

Hi, sorry to hear about your trouble with your mark IV. I have a MK IV combo from 1990 ( bought it new in january 1991 ) and I have the complete schematics, I got from the German Mesa Boogie distributor in 1992. According to this schematic, I can say the following: switching matrix section 2...

Hi, as already mentioned here, the 200 W EVM 12 L is a excellent speaker. But if one owns a combo version like me ( I have a MK IV combo with the Black Shadow EVM 12 L ), for some sounds and styles may be the EV produces a somehow too tight , focused sound, especially with a Thiele cab if used...

Hi, I also want to say, that it is important to find out the real reason for the blown fuse. Please remember, you told us, that you noticed a smell of burning over a minute. Rarely smell is caused by a blown fuse itself. For example, their are screnngrid resitors at the two outer power tubes (...